The present invention relates to an electrical connector, and particularly to a zero insertion force (ZIF) connector having contacts which ensure improved signal transmission between an IC package and a circuit board.
Conventional ZIF connectors adapted for electrically connecting an IC package to a circuit board are disclosed in Taiwan Patent Application Nos. 83214436 and 86302100. Referring to FIGS. 1A and 1B, a conventional connector comprises a dielectric base 80, a slidable cover 81 fixed to the base, a cam lever 82 attached between aligned side edges of the base 80 and the cover 81 for driving the cover to slide along a top surface of the base 80, and a plurality of contacts 83 received in corresponding contact receiving passageways 801 defined in the base 80.
Each contact 83 comprises a base plate 831, a curved portion 832 extending from a lower edge of the base plate 831, and a connecting leg 833 downwardly extending from the base plate 831 for electrically connecting with a circuit board (not shown). The curved portion 832 has a pair of curved arms (not labeled) distanced from each other at the lower edge of the base plate 831 and connecting with each other at opposite ends thereof. The curved portion 832 forms a wide gap 834 adjacent to a narrow gap 835, and a pair of flanges 836 inwardly projecting from a junction between the wide gap 834 and the narrow gap 835. When the IC package (not shown) is positioned on the cover 81, pins of the IC package are received in the wide gaps 834 of the corresponding contacts 83. Due to the sliding movement of the cover 81 driven by the cam lever 82 along the top surface of the base 80, the pins are driven to move from the wide gaps 834 into the narrow gaps 835 by the guidance of the flanges 836. Thus, the pins of the IC package electrically connect with the corresponding contacts 83 of the ZIF connector.
However, the pins of the IC package may be improperly disposed in the corresponding pin receiving passageways of the cover 81, so that the pins may not be positioned in the center of the corresponding wide gaps 834. Thus, when the pins are driven to move from the wide gaps 834 into the narrow gaps 835, each pin may only contact a single curved arm whereby the single curved arm may be burdened with too large a force, which may break the single arm resulting in poor signal transmission through the connector.
Furthermore, the symmetrical design of the conventional contact 83 usually provides a pair of symmetrical guiding portions such as the curved arms to contact the corresponding pin of the IC package. Thus, frictional forces exerted on the pins are simultaneously applied by both curved arms thereby greatly increasing resistance and hindering insertion of the pins into proper contact positions. The increased resistance may wear away a metal plate coating on the pins and the contacts resulting in poor signal transmission.
In addition, when the contacts 83 are soldered to a circuit board (not shown), the solder pads 833 of the contacts 83 are apt to become misaligned due to different thermal expansions between the base 80 and the circuit board resulting from the different coefficients of thermal expansion (CTE) thereof. The misalignment of the solder pads 833 of the contacts 83 results in unstable and unreliable signal transmission through the connector.